Memory is one type of integrated circuitry, and is used in systems for storing data. Memory is usually fabricated in one or more arrays of individual memory cells. The memory cells are configured to retain or store information in at least two different selectable states. In a binary system, the states are considered as either a “0” or a “1”. In other systems, at least some individual memory cells may be configured to store more than two levels or states of information.
Integrated circuit fabrication continues to strive to produce smaller and denser integrated circuits. Accordingly, there has been substantial interest in memory cells that can be utilized in structures having programmable material between a pair of electrodes; where the programmable material has two or more selectable resistive states to enable storing of information. Examples of such memory cells are resistive RAM (RRAM) cells, phase change RAM (PCRAM) cells, and programmable metallization cells (PMCs)—which may be alternatively referred to as a conductive bridging RAM (CBRAM) cells, nanobridge memory cells, or electrolyte memory cells. The memory cell types are not mutually exclusive. For example, RRAM may be considered to encompass PCRAM and PMCs. Additional example memory includes ferroelectric memory, magnetic RAM (MRAM) and spin-torque RAM.
Programmable memory cells of the types described above may be highly scalable and thus suitable for utilization in future generations of memory. However, problems are encountered in attempting to utilize such memory cells. For instance, the memory cells may be “leaky”; and accordingly may be paired with select devices in order to better control current flow to and from the memory cells.
An example prior art memory array 1 is shown in FIG. 1. The memory array 1 comprises a plurality of memory units 2, each including a memory cell 3 and a select device 4. The memory cells 2 are interposed at cross-points between rows 6 (also called wordlines or access lines) and columns 5 (also called bitlines or sense lines). In each memory unit 2, the memory cell 3 has a first terminal connected to a wordline 6 and a second terminal connected to a select device 4. The select device 4 has a second terminal connected to a bitline 5.
The select devices may be considered to be switchable components (or switching components), in that they may switch a circuit from an “open” configuration to a “closed” configuration. Individual memory cells may be selected by closing an adjacent switching component while creating a voltage differential between a wordline and a bitline.
It is desired to develop improved switching components, and in some aspects to develop improved switching components suitable for utilization as select devices.